Aircraft typically include a plurality of flight control surfaces that, when controllably positioned, guide the movement of the aircraft from one destination to another. The number and type of flight control surfaces included in an aircraft may vary, but typically include both primary flight control surfaces and secondary flight control surfaces. The primary flight control surfaces are those that are used to control aircraft movement in the pitch, yaw, and roll axes, and the secondary flight control surfaces are those that are used to influence the lift or drag (or both) of the aircraft. Although some aircraft may include additional control surfaces, the primary flight control surfaces typically include a pair of elevators, a rudder, and a pair of ailerons, and the secondary flight control surfaces typically include a plurality of flaps, slats, and spoilers.
The positions of the aircraft flight control surfaces are typically controlled using a flight control surface actuation system. The flight control surface actuation system, in response to position commands that originate from either the flight crew or an aircraft autopilot, moves the aircraft flight control surfaces to the commanded positions. In most instances, this movement is effected via actuators that are coupled to the flight control surfaces. Though unlikely, it is postulated that a flight control surface actuator could become jammed, uncontrollably free, or otherwise inoperable. Thus, some flight control surface actuation systems are implemented with redundant actuators coupled to a single flight control surface.
In many flight control surface actuation systems the actuators are hydraulically powered. With these systems, the aircraft typically includes two or three redundant hydraulic systems to power to the actuators, which ensures a sufficiently low probability of loss (e.g., <10−9). It is presently a goal to reduce hydraulic system redundancy. One way that has postulated to meet this goal is to implement actuator redundancy using electrically-powered actuators as the redundant actuators. While this would seemingly be a straightforward solution, it nonetheless can present certain drawbacks, particularly with the concurrent on-going move to implement composite surfaces. More specifically, presently proposed composite surfaces can exhibit little ability to sink heat. As a result, coupling electrically and hydraulically powered actuators to the same surface can present difficulties. For example, using electrically and hydraulically powered actuators may result in increased weight as a result of the heat sinking that may be needed on the composite structure. This can be most pronounced when implementing an active/active system architecture, which typically provides reduced weight and enhanced fault suppression capability as compared to, for example, an active/standby architecture.
Hence, there is a need in the art for a system and method of implementing suitably redundant aircraft flight control surface actuation control that does not increase overall system weight and/or can be implemented with composite structures and/or that provides an adequately low probability of component loss. The present invention addresses one or more of these needs.